1. Field of the Invention
The invention relates to a tool exchanging apparatus, equipped with a machining center, which shortens a tool exchange time period.
2. Description of the Prior Art
Since the economic situation has recently become serious, demand for increasing productivity has become strong. Therefore, it is very important to reduce processing time and to save energy.
Machining centers have been developed in order to cope with this trend. Work pieces are processed by exchanging a tool mounted on a main spindle housing by means of a change arm unit in machining centers. Machining centers which process work pieces in such a manner are operated in accordance with the control program as shown in FIG. 6 of the accompanying drawings, reference to which will now be made for the detailed discussion.
When the power is applied to a machining center at step F1, the machine starts its operation. After a data is initialized at step F2 and an operation command is inputted at step F3, a work piece is conveyed into the machining center at step F4, and then clamped at step F5 to a table after it has been fixed to a jig. Thereafter, a program consisting of a series of processing steps is read at step F6 from the memory, and then, it is checked at step F7 to see whether or not a tool has been mounted on a main spindle housing. If it is detected at step F8 that the tool mounted on the main spindle housing is correct, the program consisting of a series of processing steps is executed at step F9. If no tool has been mounted on the main spindle housing, a tool is mounted at step F10 on the main spindle housing. If it is detected at step F8 that the tool is correct, the program consisting of a series of the processing steps is executed at step F9. If the tool mounted on the main spindle housing is wrong, the tool is replaced at step F11 with a correct tool, and then, the program consisting of a series of the processing steps is executed at step F9. When the program consisting of a series of the processing steps terminates at step F12, it is decided at step F13 whether or not every step of the series of the processing steps has been completed. If any of the steps of the processing steps has not been executed, the number of the processing step read from the memory is advanced by one at step F14, and the program returns to step F6 wherein the processing program data consisting of a series of the processing steps are read. Thereafter, the control program from step F6 to step F13 is run, at which step a decision is made to determine whether or not all of the processing steps have been executed is repeated. If it is judged that all of the processing steps have been executed, it is determined at step F15 whether or not all of the work pieces have been processed. If all of the work pieces have not been processed, a work piece exchange is made and the number of the processing step read from the memory is returned (F16) to one, and thereafter, the program returns to step F6 at which the processing program data consisting of a series of the processing steps are read. Thereafter, the control program from step F6 to step F15 at which it is determined whether or not all of the work pieces have been processed is repeated. If it is determined that all of the work pieces have been processed, the control program terminates at step F17.
Thus, in the machining center, once the work piece is positioned and subsequently fixed to a table by a jig, the work piece can be successively processed with different tools. Thus, owing to the mechanism, the time period for processing the work piece can be shortened and labor savings can also be achieved. Further, since various kinds of processings can be accomplished without moving the work piece, a processing line can be shortened.
A conventional tool exchange method is accomplished in accordance with the tool exchange program as shown in FIG. 7. In detail, when a tool exchange program starts at step F18, a tool magazine which houses tools is rotated at step F19. The tool magazine continues to rotate until it is confirmed at step F20 that the tool (specified tool) used in the processing step has been rotated to the position where it is to be taken out. If it is detected that the specified tool has been rotated to the position where it is to be taken out, a change arm is moved in a direction (leftwards in this case) towards the tool magazine. The specified tool is caught by the change arm at one end thereof at step F21. Thereafter, a drive cylinder allows only the change arm to advance to take out the specified tool at step F22. Next, it is detected at step F23 whether or not the main spindle housing is positioned at the point where a tool on the main spindle housing is exchanged with the specified tool supported by the change arm. It is usual that, before this step F23 takes place, the main spindle housing has been moved from the position, where the work piece is positioned, back to the tool exchange position by a main spindle forward-and-backward driving unit. If the main spindle housing has not been retracted to the tool exchange position, the main spindle housing is retracted to the tool exchange position at step F24, and, after it has been confirmed at step F23 that the main spindle housing is on the tool exchange position, the change arm is moved toward the main spindle housing, namely, in a rightward direction, so that the tool on the main spindle housing is caught by the change arm at the other end thereof at step F25. Thereafter, the change arm is advanced from the tool exchange position to take the tool out of the main spindle housing at step F26, and then, is turned to position the specified tool in front of the main spindle housing at step F27, and next, retracted to the tool exchange position to fix the tool in the main spindle housing at step F28. Next, the change arm is moved toward the left at step F29 to release the tool from the change arm at step F30, and, at step F31 and after the change arm has reached the region where the change arm does not interfere with the main shaft, a command for starting the execution of the program of the process step is issued at step F32. Then the program for a series of processing steps is executed at step F9. The change arm continues a movement (at steps F33 and F34) toward the left until the tool taken out of the main spindle housing is positioned on the center line of the tool pot in the magazine. If it is detected at step F35 that the tool taken out of the main spindle housing is on the center line of the tool pot in the magazine, the magazine is advanced to house the tool therein at step F36. After the tool has been housed in the magazine, the change arm is moved at step F37 toward the right to release, at step F38, the tool housed in the magazine, and then, returns at step F39 to the neutral position where the change does not interfere with tools in the magazine as well as the main spindle housing. A tool exchange program terminates at step F40 when the change arm is returned to the neutral position.
The tool exchange apparatus of the above-described conventional machining center does not permit a change arm unit to move in the direction in which the main spindle housing moves. Therefore, the tool exchange position is set at a position backward from a work piece where the tool does not interfere with other members such as a work piece in the machining center when the tool, which is longest in the direction in which the main spindle housing moves forward and backward, is turned with the tool held by the change arm. Such a machining center has been disclosed in, for example, Japanese Patent Publication No. 10387/1976. In such a machining center, the main spindle housing is retracted to a tool exchange position distant from a work piece even when tools which are short, in the direction in which the main spindle housing moves forward and backward, are exchanged. This has caused the problem that the main spindle housing is ineffectively moved, and thus, time is wasted even when tools, which are short in the direction in which the main spindle housing moves forward and backward, are exchanged.